angular js - point ng-model to one property of an object initially, but sync back to another

I have a kendo ui grid, where each row is editable, and in a specific column I want to sync the inputs data to the underlying grid data (an array of objects) while the user is typing, and bind the input value to one specific property on the data Item,

amount

in this case. I have accomplished that first part using ng-model. When the user clicks on a button to pay, I want

amount

(also a property in the data item) to be set to another property's value (which also is in the same object) which is called

amountDue.due

.

This is what I tried, it is working OK in the first case where the user has not clicked on the button to pay. However, I can't figure out the case when the user has clicked pay - the nested if below is not working. in angularjs, how do I point an ng-model to one property of an object (or in this case a nested property,

amountDue.due

) on init and have this saved in another property (in this case

amount

)?

So in this case if

paymentClicked

I want the ng-model to take an initial value of

amountDue.due

, but I want that value saved in the

amount

property. I am trying to do this with angular as much as possible and not kendo.